Speculation that silicon-based semiconductor manufacturing processes will encounter a miniaturization limit has led to a large research effort in molecular electronics, where molecular monolayers are used as active switching components. In the case of active devices, in particular, wherein current is driven through the molecules, two-terminal molecular switches have been the subject of much research, with switching behavior reported for several systems. However, there are perceived uncertainties about the switching mechanisms, the local environment, as well as temperature, which can potentially affect the conduction through molecular junctions.
Whereas organic films deposited from solution or by sublimation have been used in organic field-effect transistors with some success, such devices are not molecular-monolayer based. In most molecular-monolayer-based systems, the molecules being tested are first self-assembled onto a metallic electrode and then a second metal electrode is evaporated on top of them to create a metal-molecular-monolayer-metal sandwiched device.
Several persistent problems arise in these ultrathin sandwich structures. First, as the top electrode is vapor-deposited onto the self-assembled monolayer, energetic metal atoms can degrade the molecules. Second, the metal often penetrates the molecular monolayer to form metallic current paths, thereby short circuiting the device.
Owing to pinhole defects in the self-assembled monolayer, this problem can remain even upon cryogenic cooling during the top-metal evaporation step. For other approaches, such as the mercury-drop top-contact or scanning-probe-microscopy methods, it is believed to be unlikely that metal nanofilaments form when the device is first assembled, and consistent results have been recorded in these systems. However, there are cases when a voltage is applied during the testing where electrode melting occurs; therefore, even if metallic nanofilaments are not initially formed, they can result upon use of the device. The formation of metal nanofilaments can be confused with molecular switching, and current-voltage-temperature (I(V,T)) measurements are needed to distinguish the molecular versus metallic nanofilament switching mechanisms.
In sum, it has been demonstrated in the prior art that metal nanofilaments cause problems in some molecular electronics testbeds.